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Plasticized polyvinyl chloride (PVC) gel has large deformation under an applied external electrical field and high driving stability in air and is a candidate artificial muscle material for manufacturing a flexible actuator. A porous PVC gel actuator consists of a mesh positive pole, a planar negative pole, and a PVC gel core layer. The current casting method is only suitable for manufacturing simple 2D structures, and it is difficult to produce multilayer porous structures. This study investigated the feasibility of a 3D-printed carbon nanotube-doped silicone electrode for manufacturing multilayer porous PVC gel artificial muscle. Carbon nanotube-doped silicone (CNT-PDMS) composite inks were developed for printing electrode layers of PVC gel artificial muscles. The parameters for the printing plane and mesh electrodes were explored theoretically and experimentally. We produced a CNT-PDMS electrode and PVC gel via integrated printing to manufacture multilayer porous PVC artificial muscle and verified its good performance. [ABSTRACT FROM AUTHOR]

Flexible wearable devices have attracted wide attention in capacious fields because of their real-time and continuous monitoring of human information. The development of flexible sensors and corresponding integration with wearable devices is of great significance to build smart wearable devices. In this work, multi-walled carbon nanotube/polydimethylsiloxane-based (MWCNT/PDMS) resistive strain sensors and pressure sensors were developed to integrate a smart glove for human motion/perception detection. Firstly, MWCNT/PDMS conductive layers with excellent electrical and mechanical properties (resistivity of 2.897 KΩ · cm, elongation at break of 145%) were fabricated via a facile scraping-coating method. Then, a resistive strain sensor with a stable homogeneous structure was developed due to the similar physicochemical properties of the PDMS encapsulation layer and MWCNT/PDMS sensing layer. The resistance changes of the prepared strain sensor exhibited a great linear relationship with the strain. Moreover, it could output obvious repeatable dynamic response signals. It still had good cyclic stability and durability after 180° bending/restoring cycles and 40% stretching/releasing cycles. Secondly, MWCNT/PDMS layers with bioinspired spinous microstructures were formed by a simple sandpaper retransfer process and then assembled face-to-face into a resistive pressure sensor. The pressure sensor presented a linear relationship of relative resistance change and pressure in the range of 0–31.83 KPa with a sensitivity of 0.026 KPa−1, and a sensitivity of 2.769 × 10−4 KPa−1 over 32 KPa. Furthermore, it responded quickly and kept good cycle stability at 25.78 KPa dynamic loop over 2000 s. Finally, as parts of a wearable device, resistive strain sensors and a pressure sensor were then integrated into different areas of the glove. The cost-effective, multi-functional smart glove can recognize finger bending, gestures, and external mechanical stimuli, which holds great potential in the fields of medical healthcare, human-computer cooperation, and so on. [ABSTRACT FROM AUTHOR]

The prospects of endowing artificial robotics or devices with increasingly complex and emergent life‐like behaviors have attracted growing interest in the soft functional materials that mimic the versatile motions of living creatures in the iridescent nature. However, despite the flourishing achievements so far, soft actuators capable of sensitive multi‐stimulus responses and self‐sustainable movements, have been extensively pursued to reduce control complexity yet remains a challenging target. Here, through material‐structural synergistic design incorporating stress‐mismatching structure, high pseudo‐negative coefficient of thermal expansion of perfluoro‐sulfonic acid ionomer, comprehensive converting properties of carbon nanotube, and anisotropic large thermal expansion of PE polymer, an ionomer‐based bilayer actuator is proposed, presenting high‐performance actuation of various forms and nice stability, responsive to light (including sunlight without focusing, LED light), low voltage, mild heating, and humidity/solvent change. With a built‐in structural feedback loop, the actuation performances are further explored to realize intelligent systems, including: 1) self‐sustainable locomotion under sunlight irradiation with adjustable photophobic and phototropic direction as well as adaption to different topographies and loading conditions, 2) self‐sustainable oscillation and solar‐electric generating, and 3) bionic floristic reaction according to environmental change. These diversified actuation modes allow promising following‐up designs for bio‐hybrid soft robotics fueled by and harmonized with natural environments. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) film possesses excellent mechanical and piezoresistivity, which may act as a sensor for process monitoring and reinforcement of the final composite. This paper prepared CNT/epoxy composite film via the solution dipping method and investigated the electrical resistance variation (ΔR/R0) of CNT/epoxy composite film during the curing process. The temperature dependence of electrical resistance was found to be closely related to resin rheological properties, thermal expansion, and curing shrinkage. The results show that two opposing effects on electrical resistivity occur at the initial heating stage, including thermal expansion and condensation caused by the wetting tension of the liquid resin. The lower resin content causes more apparent secondary impregnation and electrical resistivity change. When the resin viscosity remains steady during the heating stage, the electrical resistance increases with an increase in temperature due to thermal expansion. Approaching gel time, the electrical resistance drops due to the crosslink shrinkage of epoxy resin. The internal stress caused by curing shrinkage at the high-temperature platform results in an increase in electrical resistance. The temperature coefficient of resistance becomes larger with an increase in resin content. At the isothermal stage, an increase in ΔR/R0 value becomes less obvious with a decrease in resin content, and ΔR/R0 even shows a decreasing tendency. [ABSTRACT FROM AUTHOR]

As emerging smart polymers, ionic polymer-metal composites (IPMCs) are playing more and more important roles as promising candidates for next-generation actuators in terms of academic interest and industrial applications. It is reported that the actuation behaviors of IPMCs are dependent on the electrochemical kinetic process between metal/polymer interfaces to a great extent. Thus, the fabrication of tailored metal/polymer interface electrodes with large surface areas and superior interface characteristics is highly desirable in improving the actuation performance of IPMCs, which is still technologically critical for IPMCs. In this contribution, we developed a novel fabrication technology for carbon/metal composite electrodes with a superior interface structure and characteristics to optimize the actuation behaviors of IPMCs by exploiting the synergistic effect of combining a sulfonated multi-walled carbon nanotube (SCNT)/Nafion hybrid layer with nanodispersed Pd particles. The improved IPMCs showed significantly enhanced capacitance characteristics and highly facilitated charge–discharge processes. Moreover, their actuation behaviors were greatly improved as expected, including approximately 2.5 times larger displacement, 3 times faster deformation speed, 4 times greater output force, and 10 times higher volume work density compared to those of the IPMCs with traditional electrode structures. The advantages of the developed SCNT/Pd-IPMCs will greatly facilitate their applicability for artificial muscles. [ABSTRACT FROM AUTHOR]

Sodium ion batteries (SIBs) are promising energy storage systems because sodium is a low cost and abundant resource. Appropriate electrode materials with high performance are a prerequisite to satisfy demand for efficient SIBs. Heterostructured electrodes show high specific capacity and rate capacity for SIBs owing to the synergistic effect of multiple components compared with a single component. Here, heterostructured binary metal-sulfide CoS2/NiS2 compounds encapsulated in bamboo-like carbon nanotubes (CoS2/NiS2@B-CNT), were prepared by pyrolysis and sulfidation procedures. The heterostructured anode material demonstrates a high capacity of 625.8 mA h g−1 at 0.1 A g−1, a distinguished rate capacity (491.6 mA h g−1 at 10 A g−1), and stable cyclic property (497.6 mA h g−1 at 5 A g−1 after 1000 cycles, 93.0% capacity retention). This design of a heterostructure offers a new avenue to develop anode materials with high performance for SIBs. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) graphitic carbon nitride (g-C3N4) nanosheets show brilliant application potential in numerous fields. Herein, a membrane with artificial nanopores and self-supporting spacers was fabricated by assembly of 2D g-C3N4 nanosheets in a stack with elaborate structures. In water purification the g-C3N4 membrane shows a better separation performance than commercial membranes. The g-C3N4 membrane has a water permeance of 29 L m−2 h−1 bar−1 and a rejection rate of 87 % for 3 nm molecules with a membrane thickness of 160 nm. The artificial nanopores in the g-C3N4 nanosheets and the spacers between the partially exfoliated g-C3N4 nanosheets provide nanochannels for water transport while bigger molecules are retained. The self-supported nanochannels in the g-C3N4 membrane are very stable and rigid enough to resist environmental challenges, such as changes to pH and pressure conditions. Permeation experiments and molecular dynamics simulations indicate that a novel nanofluidics phenomenon takes place, whereby water transport through the g-C3N4 nanosheet membrane occurs with ultralow friction. The findings provide new understanding of fluidics in nanochannels and illuminate a fabrication method by which rigid nanochannels may be obtained for applications in complex or harsh environments. [ABSTRACT FROM AUTHOR]

Abstract: The nanotube structure has unique advantages, such as a large electroactive surface area and shorter diffusion pathway for ions/electrons for energy storage. In this paper, we fabricated a novel supercapacitor electrode material based on a composite material with a hollow tube‐on‐tube architecture. This architecture, which was derived from the sustainable Juncus roemerianus, consisted of nickel cobalt sulfide nanotubes coating the exterior and interior of carbon tubes. The obtained hollow tube‐on‐tube structure is similar to a reservoir, in which ions/electrons can diffuse via a bi‐directional method and supply and transfer to the carbon tube interface. Consequently, this structure can probably provide more electrochemically active sites for its application in high‐performance asymmetric supercapacitors (ASCs). The assembled ASC device also presents superior specific capacitance (83 F g−1 at the current density of 0.5 A g−1), high energy density (27.7 Wh kg−1 at a power density of 263.6 W kg−1), and good cycling stability (72.23 % capacitance retention after 3000 cycles). Therefore, the NiCo2S4/bio‐carbon electrode with hollow tube‐on‐tube structure is not only a promising electrode material, but also can be applicable to energy storage and conversion devices. [ABSTRACT FROM AUTHOR]

A nano-carbon composite, consisting of a graphene aerogel-carbon nanotube (CNT) film, is constructed by coating a strong and flexible CNT film onto the surface of a porous graphene aerogel core. The prepared gradient composite, ultralight and strong, can carry objects more than 15,000 times its own weight, exhibiting impressive compression resistance. Compared to the original graphene aerogel, the composite exhibits 8–9-fold increased values in its elastic modulus and compressive strength at a strain of 20% and an approximately 10-fold increase in electrical conductivities in the axial direction. In addition, the elastic recovery ability after compressive deformation and the ability to preserve liquid are also improved. [ABSTRACT FROM AUTHOR]

As a kind of 2D macroscopic assembly of carbon nanotube (CNT), CNT film fabricated from CNT array performs outstanding properties and potential applications in many areas. For CNT film fabricated from spinnable array, the nanotube's alignment and packing density are two important factors for improving the properties. In this work, inspired by the unique transferring process, we intended to adjust the CNT stacking status in the film via optimizing the winding process and assisting appropriate post-treatment. Array-based CNT films with different winding parameters were fabricated to study the effect of winding speed and winding thickness on the film's tensile properties. It is revealed that related with the drawing force, the winding speed plays an important role in tuning CNTs arrangement in nanotube sheet. Within a certain range, increasing speed is helpful to straighten and uniformly disperse nanotubes, and further improve the tensile properties of the film. While for winding thickness, appropriate reducing thickness is favorable for sheets compaction and decreasing defects, which further enhance the properties. Additionally, combining the low elongation feature of array-based CNT film, little-ratio post-stretching is applied on the films, which is also proved to be efficient for densifying and aligning, stimulating the film stronger and more conductive simultaneously. [ABSTRACT FROM AUTHOR]

Highlights Carbon nanotube (CNT) film is favored in structural health monitoring of advanced composite materials, primarily due to its commendable mechanical properties and piezoresistive properties. Nonetheless, floating catalytic chemical vapor deposition (FCCVD) is an attractive method for fabrication of CNT films, and the electrical response to strain of FCCVD‐prepared CNT films is impeded by high aspect ratio and lamellar packing structure. For this purpose, FCCVD CNT films were modified by HCl dissolving Fe impurities, nano‐SiO2 particles doping and freeze‐drying in combination to increase the spacing between CNTs and its networks as well as their strain sensitivities. It showed that the gauge factor (GF) according to the variation of resistance (ΔR/R0) of the co‐modified film (CNT‐HCl‐SiO2 film) was up to 15.6 for the tensile strain at the bottom surface of unidirectional carbon fiber reinforced plastic (CFRP) laminates during the process of bending tests. The bending cycle experiment of the CFRP showed relatively stable changes of ΔR/R0 with the strains for CNT‐HCl‐SiO2 film, while that of the pristine CNT film (CNT‐HCl‐0 film) displayed unstable non‐monotonic changes and that of HCl purified CNT film (CNT‐HCl‐10 film) revealed a gradual declining tendency. Moreover, the ΔR/R0 of CNT‐HCl‐SiO2 film exhibited excellent sensitivity to the strains of multiple bistable‐deformations of cross‐ply CFRP laminates. Strain gauge analysis indicated that a 51% increase of ΔR/R0 of CNT‐HCl‐SiO2 film at the 90° layer surface corresponded to the average strain of 434 με, meanwhile a 37% increase of ΔR/R0 of the CNT film at the 0° layer surface corresponded to the strain of averagely −173.9 με, and both exhibited super high GFs of 1175 and 2108, respectively. Based on this high sensitivity, CNT‐HCl‐SiO2 film also had the ability to predict the release of residual stress during the demoulding process of CFRP. Even SiO2 dispersion in CNT film, increased the pristine film thickness by 10 times GF of CNT‐HCl‐SiO2 film increased by 68% than CNT‐HCl‐0 film and by 164% than CNT‐HCl‐10 film SiO2 doping significantly improved the stability of the CNT film's ΔR/R0 with temperature and strain CNT‐HCl‐SiO2 film has the ability to monitor the deformation and residual stress of CFRP [ABSTRACT FROM AUTHOR]

This paper developed an out‐of‐plane permeability measuring method by utilizing conductive carbon nanotube (CNT) buckypaper and its piezoresistivity. A series of CNT sensors was arranged orderly in different interlaminar regions to achieve infiltration monitoring for both glass and carbon fabrics. The response of electrical resistance to flow front was investigated, and the out‐of‐plane unsaturated permeabilities at different fiber volume fractions were further calculated according to the monitoring results of those CNT sensors. The results show that the electrical resistance variation and time curves can be divided into three stages, including the initial baseline stage, rapid growth stage, and smooth growth stage. For most CNT sensors, ΔR/R0 becomes higher than 15% and 20% at the end of rapid growth stage and smooth growth stage, respectively. These CNT sensors show the sudden increase of electrical resistance successively along the infiltration direction. The squared infiltration distance and time show linear relationship, and the out‐of‐plane unsaturated permeability is further calculated based on Darcy's law. The out‐of‐plane unsaturated permeability of EW100 glass fabric is measured to be 4.76 × 10−13 m2 at a fiber volume faction of 63.0%. The unsaturated permeability increases with decreasing fiber volume fraction, and the carbon fabric with smaller fiber diameter shows smaller unsaturated permeability at the approximate fiber volume fraction. [ABSTRACT FROM AUTHOR]

The interface properties between surface grown carbon nanotubes carbon fiber (CNTs‐CF) and epoxy resin were investigated by different modification methods. The X‐ray photoelectron spectrometer probations show that the pristine CNTs‐CF has very low contents of both oxygen element and active carbon element. Taking the naked carbon fiber (CF) without CNTs grown as a reference, the interfacial shear strength (IFSS) of CNTs‐CF/epoxy is only 5.6% higher. After heat treatment, chemical modification and sizing treatments, the surface chemical activity of CNTs‐CF is improved considerably. In contrast with the IFSS of standard CF/epoxy, the interfacial strength of chemical‐treated CNTs‐CF‐E1/epoxy is increased to 122.8 MPa by 29.7%. The increasing content of the epoxy active groups at the modified CNTs‐CF‐E1 surface is conducive to forming covalent bonds between the epoxy resin and the CNTs‐CF‐E1 surface particularly the activated nanotube surface. The enhancement of CNT/epoxy interface is beneficial to the over whole interface property of the composites. Hence, the compressive and torsion strength of sizing CNTs‐CF‐E1 bundle combined with epoxy resin are increased by 32.4% and 14.1%, respectively. The SEM images show the failure morphologies of different modification methods, and the enhancement mechanism of multiscale interface is further clarified. Compared with chemical treatment, heat treatment can remove the inert amorphous carbon on the CNTs‐CF fiber surface and improve the interface adhesion of CNT/epoxy and CF/epoxy, and surface sizing treatment improves the CF/epoxy interface. The enhancement mechanisms of these modified CNTs‐CFs/epoxy should be ascribed to the competition and synergetic effects of the multiscale interfaces, including CNT/CF, CNT/epoxy, and CF/epoxy. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) macroscopic assembly, as a promising candidate for the protective and anti-collision materials, has attracted lots of researchers to explore its mechanical behavior under different loading rates. In this paper, the loading-rate dependent mechanical behavior of CNT film and its composite with bismaleimide (BMI) matrix is investigated. The pristine CNT film shows decreased tensile strength by 33.8% when the loading rate increases from 0.05 mm/min to 40 mm/min. An obvious necking extending phenomenon is observed in the CNT film during the tensile test under lower tensile rates, e.g. 0.05 mm/min and 0.5 mm/min. However, the random composite film and the oriented composite film both display increased tensile strength, by 58.2% and 35.7% respectively, with the increasing loading rate from 0.05 mm/min to 40 mm/min. The different loading-rate dependence of tensile behavior is ascribed to the different tensile-induced motions of CNTs and CNT bundles in composite film. Moreover, strain rate sensitivity coefficients of different film are calculated according to a simplified Johnson-Cook model. The results suggest that the pristine CNT film with the strain rate sensitivity coefficient of − 0.0941 has a high loading-rate sensitivity, meanwhile polymer infiltration and oriented alignment can weaken the loading-rate sensitivity of CNT film. [ABSTRACT FROM AUTHOR]